We are working on proper documentation; Work-in-progress on that documentation is here: Behavior Tree Documentation. I plan to keep updating it while we’re getting ready to “release” Behavior Trees from the “Experimental” section.
As soon as it’s in more complete form, we’ll move it to the official documentation page.
We’ve also got some samples in progress (Mieszko Z. just made a very cool sample level with a purely blueprint (no code) behavior tree example). I’m hoping to combine samples and some intro documentation to be able to make some videos starting with a video of all the basics for new users.